Helium formation from hydrogen

The majority of the Universe is made from hydrogen and helium produced during the Big Bang, although some He has been made subsequently. The relative cosmic abundance of some of the elements relevant to the formation of life is given in Table 1.2, with all elements heavier than H, He and Li made as a result of fusion processes within stars, as we shall see later. The cosmic abundance is assumed to be the same as the composition of the Sun. 

Ammonia decomposes on zeolites (9), and the effect of this decomposition on the chlorobenzene reaction may be important. Thus, the activity of CuY zeolite for ammonia decomposition was studied. Helium was used as a carrier gas, 1 ml of ammonia was injected, and the extent of ammonia decomposition was determined as a function of temperature. The decomposition was 2.4% at 350°C, 7.8% at 450° C, and 24% at 550° C. The apparent activation energy of ammonia decomposition was estimated at 13 kcal/mole. The activation energy of ammonia decomposition is close to that of benzene formation from chlorobenzene and ammonia. Thus, benzene formation results from the reaction of chlorobenzene and hydrogen formed by the decomposition of ammonia. 

Khan, P., Mazumdar, P.S. and Ghosh, A.S. (1985). Positronium formation in the n = 2 level in positron scattering from hydrogen and helium atoms. Phys. Rev. A 31 1405-1414. 

Mandal, P., Guha, S. and Sil, N.C. (1979). Positronium formation in positron scattering from hydrogen and helium atoms the distorted-wave approximation. J. Phys. B At. Mol. Phys. 12 2913-2924. 

Photodecomposition of the benzenesulfonamide derivative 183 in aqueous solution was investigated by irradiation from a 254 nm low pressure lamp under a helium atmosphere. Homolytic fission of the S-N bond gives arylsulfonyl and arylsulfonylamino radicals. Gyclization from the latter radical via C-N bond formation and hydrogen atom abstraction afforded the /3-sultam 47 in 7% yield. Other photodissociation processes resulted in the formation of compounds 184-186 (Scheme 59) <2002JPH109>. 

R.C. Tolman, Thermodynamic treatment of the possible formation of helium from hydrogen, Journal of the American Chemical Society 44 (1922) 1902-1908, on 1905. 

Modem astrophysieal views incline to the belief that in the stars there is going on a synthetic formation of the chemical elements from hydrogen and helium. Possibly the starting-point in these syntheses is nebulium, the first step being its conversion into hydrogen, and the second the association of the hydrogen to form helium. Further association of the helium to elements of even atomic numbers would constitute the next... 

The net result of this cycle is the formation of helium from hydrogen, with gamma rays, positrons, and neutrinos as byproducts. In addition, even heavier elements are formed ... 

The principal products of helium burning are thus 0 and C. That these are the third and fourfti most abundant isotopes in the Solar System (after H and He) shows that helium burning is a significant player in the formation of the elements. Other key products of helium burning are 0 and Ne produced fi om left over from hydrogen burning ... 

Nucleosynthesis is the formation of elements. Hydrogen and helium were produced in the Big Bang all other elements are descended from these two, as a result of nuclear reactions taking place either in stars or in space. Some elements—among them technetium and promethium—are found in only trace amounts on Earth. Although these elements were made in stars, their short lifetimes did not allow them to survive long enough to contribute to the formation of our planet. However, nuclides that are too unstable to be found on Earth can be made by artificial techniques, and scientists have added about 2200 different nuclides to the 300 or so that occur naturally. 

The formation of the planets around the proto-sun initially started as a simple accretion process, aggregating small particles to form larger particles. This process was common to all planets, even the gas giants Jupiter and Saturn and to a lesser extent Neptune and Uranus. The planetesimals form at different rates and as soon as Jupiter and Saturn had reached a critical mass they were able to trap large amounts of hydrogen and helium from the solar nebula. The centres of Jupiter... 

These results indicate the formation of 1-hexene from -hexane in both helium and hydrogen. The absence of cyclohexane is due to the lack of its formation and not to its rapid further reaction to benzene. The rate of hexene aromatization is more rapid than that of hexane (52, 54). 

By its great mass, the Sun constitutes the major part of the Solar System. In this sense, it is more representative than the planets, which have been the scene of intensive chemical fractionation. The composition of the solar photosphere can thus be compared with the contents of meteorites, stones that fall from the sky, a second source of information on the composition of the protosolar cloud, provided that volatile elements such as hydrogen, helium, carbon, nitrogen, oxygen and neon are excluded. Indeed, the latter cannot be gravitationally bound to such small masses as meteorites and tend to escape into space over the long period since their formation. 

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